The present invention relates to conditioning sub-assemblies for conditioning a polishing pad (hereinafter referred to as "pad conditioning") that are employed in chemical-mechanical polishing (sometimes referred to as "CMP") of substrates. More particularly, the present invention relates to conditioning sub-assemblies that provide conditioning surfaces that conform to the shape of the polishing pad during conditioning of a polishing pad.
As is well known in the art, an end effector and a conditioning disk are integral components of a conditioning sub-assembly, which is typically employed during conditioning of a polishing pad used for chemical-mechanical polishing (CMP) of substrates. CMP typically involves mounting a substrate, such as a semiconductor wafer, faced down on a holder and rotating the wafer face against a polishing pad mounted on a platen, which in turn rotates or orbits about an axis. A slurry containing a chemical that chemically interacts with the facing wafer layer and an abrasive that physically removes that layer is flowed between the wafer and the polishing pad or on the pad near the wafer. In semiconductor wafer fabrication, this technique is commonly applied to planarize various wafer layers such as dielectric layers, metallization layers, etc.
FIG. 1A shows some major components of a CMP apparatus such as an AvantGaard 676, which is commercially available from Integrated Processing Equipment Corporation (IPEC) of Phoenix, Ariz., disposed beneath a polishing pad 102. Polishing pad 102 includes a plurality of slurry injection holes 120 and adheres to a flexible pad backing 104, which includes a plurality of pad backing holes 1 18 aligned with slurry injection holes 120. A slurry mesh 106, typically in the form of a screen-like structure, is positioned below pad backing 104. An air bladder 108 capable of inflating or deflating is disposed between a plumbing reservoir 110 and slurry mesh 106. Air bladder 108 pressurizes to apply the required polishing force. A co-axial shaft (not shown to simplify illustration) is attached to the bottom of plumbing reservoir 110 and through which a slurry inlet (not shown to simplify illustration) is provided to deliver slurry through plumbing reservoir 110 and air bladder 108 to slurry mesh 106. Slurry is delivered to the system by an external low pressure pump. Under operation, the polishing pad "bows" or is shaped like an outwardly protruding dome as shown in FIG. 1 due to a greater force applied by air bladder 108 at a center region of polishing pad 102 than peripheral regions of polishing pad.
Unfortunately after polishing on the same polishing pad, e.g., polishing pad 102 of FIG. 1, for over a period of time, the polishing pad suffers from "pad glazing." As is well known in the art, pad glazing results when the particles eroded from the wafer surface along with the abrasives in the slurry tend to glaze or accumulate over the polishing pad. A glazed layer on the polished pad typically forms from eroded film and slurry particles that are embedded in the porosity or fibers of the polishing pad. Pad glazing is particularly pronounced during planarization of an oxide layer such as silicon dioxide layer (hereinafter referred to as "oxide CMP"). By way of example, during oxide CMP, eroded silicon dioxide particulate residue accumulates along with the abrasive particles from the slurry to form a glaze on the polishing pad. Pad glazing is undesirable because it reduces the polishing rate of the wafer surface and produces a non-uniformly polished wafer surface. The non-uniformity results because glazed layers are often unevenly distributed over a polishing pad surface.
One way of achieving and maintaining a high and stable polishing rate is by conditioning the polishing pad (hereinafter referred to as "pad conditioning") on a regular basis, i.e. either every time after a wafer or substrate has been polished or simultaneously during wafer or substrate CMP. During pad conditioning, the polishing pad is abraded to remove the glazed layer and form grooves, which facilitate slurry flow across the polishing pad and to the pad-wafer interface. FIG. 2A shows some significant components of a conditioning sub-assembly 200, which is integrated into a modern CMN system, e.g., AvantGaard 676 mentioned above. Conditioning sub-assembly 200 includes a conditioning arm 204 that is positioned above a polishing pad 102 of FIG. 1 during pad conditioning and capable of pivoting about a pivoting point 206. Conditioning arm 204, as shown in FIG. 2A, is typically longer in length than the diameter of polishing pad 102.
FIG. 2B shows a bottom view of conditioning arm 204 of FIG. 2A. The bottom surface of conditioning arm 204 includes a plurality of diamond abrasive particles 208, which are almost uniformly arranged on conditioning 204 arm such that if the conditioning arm contacts polishing pad 102, abrasive particles 208 engage a portion of the polishing pad. A manifold 210 having a plurality of openings 212 is mounted on both sides of conditioning arm 204, as shown in FIG. 2B. Openings 212 are designed to dispense a conditioning reagent on polishing pad 202 during pad conditioning and are therefore in communication with a reservoir of conditioning reagent (not shown to simplify illustration). In this configuration, openings 212 along with manifold 210 span the entire length of conditioning arm 204.
During a typical pad conditioning process, a conditioning reagent is introduced on polishing pad 102 of FIG. 2A through openings 212 of FIG. 2B and conditioning arm 204 is lowered automatically to contact polishing pad 102, which may be in orbital motion. A pneumatic cylinder then applies a downward force on conditioning arm 204 such that abrasive particles 208 of FIG. 2B engage polishing pad 102 of FIG. 2A. Conditioning arm 204 typically sweeps back and forth across polishing pad 102 like a "windshield wiper blade" from one end (shown by conditioning arm 204') of the polishing pad to another (shown by conditioning arm 204") as shown in FIG. 2A to remove the glazed or accumulated particles coated on the polishing pad surface.
FIG. 3 shows a cross-sectional view of polishing pad 102 undergoing pad conditioning as described above in reference to FIG. 2A. Beneath polishing pad 102, flexible pad backing 104, pad backing holes 118, slurry injection holes 120, slurry mesh 106, air bladder 108, and plumbing reservoir 110 are in substantially the same configuration as shown in FIG. 1.
Unfortunately, due to the bow or protruding dome shape of the polishing pad during pad conditioning, the current pad conditioning process fails to effectively condition a significant portion of polishing pad surface. FIG. 3 shows that a center region 102" of the polishing pad makes contact with abrasive particles 208, however, peripheral regions 102' of the polishing pad do not make contact with abrasive particles 208 and are not conditioned or insufficiently conditioned to remove the glazed layer (not shown to simplify illustration) on the polishing pad. Ineffective pad conditioning, therefore, fails to maintain a desirable high and stable polishing rate.
What is therefore needed is an effective pad conditioning apparatus and process, which conditions a substantial portion of the polishing pad to maintain a high and stable polishing rate.